This invention relates to a printing ink and vehicle for offset heat-set litographic printing.
In recent years, there has been a growing trend to use offset lithographic printing techniques to print on web stock as opposed to sheet stock. Because of the continuous nature of the web stock, the potential exists for significantly greater production output through the printing and drying equipment. Frequently, two or more colors are successively applied to the web, each color being printed in register and set by application of sufficient heat followed by cooling to enable the next process step such as sheeting or folding to be immediately performed. To achieve high quality printing in this process requires the applied inks to exhibit very high gloss level, rub-resistance, excellent transfer and blanket release, and sharp print quality, as is known to those in the trade.
Achieving these results necessitates reaching a web temperature of at least 250.degree.-260.degree. F. when operating at a line speed of 600 feet per minute, to dry the ink sufficiently before the web advances to the chilling stage, so that the ink does not transfer and build up on the folders, formers, and guide wheels used at the output end of the press. These web temperatures and/or line speeds are representative and could be higher or lower depending on ink coverage. The cost of heat energy to do this is substantial. If the drying temperature could be lowered or if the line speed increased, the energy savings could be large. As far as is known, this has not heretofore been accomplished, however. Further, although decreasing drying temperatures necessary is desirable, it is also important to maintain good print quality. Moreover, if an ink with lower potential drying temperatures, i.e. higher drying rates were to be developed, the more rapid rate of solvent evaporation would be expected to occur not only in the elevated temperature dryer, but also on the ink feed train of the press. This latter effect cannot be tolerated.